In recent years, research and development related to high-recording-density optical discs represented by a DVD (Digital Versatile Disc) has been actively performed. Concurrently, a CD (Compact Disc) which is conventionally commonly used is still widespread.
Consequently, research and development on a so-called compatible recorder/player capable of recording/reproducing information to/from a plurality of kinds of optical discs having different recording densities by a single information recording/reproducing apparatus has been being also performed.
Some of the above-described various optical discs employ information recording/reproducing methods (recording/reproducing standards) different from each other or have physical structures (particularly, the distance between the surface on the light beam incident side to the information recording surface) different from each other. In the compatible recorder/player, to accurately and reliably record/reproduce information to/from each of a plurality of kinds of optical discs, the kind of a target optical disc is automatically identified prior to recording/reproduction of information and, by using the result of identification, parameters and the like in actual recording/reproduction have to be set.
Various conventional techniques for identifying the kind of an optical disc have been proposed. An example of the conventional techniques is a technique (A) using the RF (Radio Frequency) level in a reproduction signal (refer to Japanese Patent Application Laid-Open Nos. H9-270167 and H9-320180).
Another example is a technique (B) using the positional relation on a focus servo, between the surface of a disc and a reflection layer for reflecting a light beam (refer to Japanese Patent Application Laid-Open Nos. H10-074356 and H10-188458).
Further another example is a technique using the amplitude of a tracking error signal according to the push-pull method (refer to Japanese Patent Application Laid-Open No. H10-302381).